Switchable fiber termination

ABSTRACT

An apparatus, system and method are provided for a switchable fiber termination (SFT) incorporated into an optical network device that responds to a test signal received via an optical network carrying data. The test signal may be a part of a multiplexed signal carrying data and is separated from the data by a wavelength division multiplexer. The SFT may be used to determine the characteristics of an optical network, including the operational status of optical network devices.

BACKGROUND INFORMATION

Technological advancements such as the Internet, video on demand,high-definition television (HDTV), video conferencing, multipletelephone lines, etc. and the need or desire for better quality videoand audio have created the demand for more and more bandwidth atbusinesses and homes. In response to this demand, telecommunicationsproviders and others began installing fiber optic telecommunicationscables with extremely large bandwidths to replace or supplementtraditional copper and coaxial systems. Fiber-optic cable is known inthe art to one of ordinary skill and is generally comprised of aplurality of fiber-optic strands and buffering material encased in oneor more layers of shielding material. Initially, because of the cost offiber optic cable, head-end equipment and terminating equipment, thefiber optic cable was extended only to large businesses and localexchange panels where service to small business, homes and otherresidential dwellings was still occurring through copper wires. However,bandwidth demand has continued to grow and costs of fiber-optic cableand equipments has decreased and consequentially, telecommunicationsproviders and others have begun to install fiber optic cable all the wayto small businesses, homes and other residential dwellings. This isgenerally referred to as fiber to the premises (FTTP).

In many instances, passive optical networks (PONs) are used to provideFTTP as well as fiber to the curb (FTTC) and fiber to the neighborhood(FTTN). PON is a fiber to the premises configuration in which unpoweredoptical splitters are used to enable a single optical fiber to servemultiple premises. The advantages to PON include that it is afiber-based transmission network that contains no active electronics andthat a single fiber may provide service to multiple premises. It is apoint-to-multipoint configuration, which reduces the amount of fiberrequired compared with point-to-point configurations. However, the verydesign that makes PONs attractive from a design and cost standpointcreates challenges when testing a PON, especially when the PON ison-line or active. Prior technologies have used a moveable mirror toselectively reflect light back into a fiber for test purposes. However,these devices reflect the light at all wavelengths back onto the fiber.This allows the fiber to be tested by an instrument at the other end ofthe fiber, but this test cannot be made without disrupting traffic onthe fiber. Also, these devices have not been designed to work in PONs.Instead they have been used in point-to-point fiber networks or FiberDistributed Data Interface (FDDI) networks (e.g., token ring).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary passive optical network (PON) used for thetransport of data;

FIG. 2 is an embodiment of a PON according to the present invention fortesting the characteristics of the optical network;

FIG. 3 illustrates an embodiment of an exemplary optical network devicethat is further comprised of an SFT according to the present invention;

FIG. 4 illustrates another embodiment of an exemplary optical networkdevice that is further comprised of an SFT according to the presentinvention;

FIG. 5 is an exemplary preferred embodiment of a SFT comprising anoptical switch and a mirror according to the present invention;

FIG. 6 is an exemplary process of using an optical network deviceequipped with a SFT to determine characteristics of an optical networkand one or more of the components that comprise the network;

FIG. 7 shows an exemplary process for a SFT according to an embodimentof the invention; and

FIG. 8 describes an exemplary process for determining characteristicsand the status of an optical network and one or more of the componentsthat comprise the optical network according to an embodiment of thepresent invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The preferred embodiments implemented according to the present inventionnow will be described more fully with reference to the accompanyingdrawings, in which some, but not all possible embodiments of theinvention are shown. Indeed, the invention (as recited by the claimsappended hereto) may be embodied in many different forms and should notbe construed as limited to the embodiments set forth herein. Rather,these embodiments are provided so that this disclosure will satisfyapplicable legal requirements. Like numbers refer to like elementsthroughout.

The preferred embodiments (or portions thereof) may be implemented as amethod, a data processing system, or a computer program product.Accordingly, an embodiment may take the form of an entirely hardwareembodiment, an entirely software embodiment, or an embodiment combiningsoftware and hardware aspects. Furthermore, implementations of thepreferred embodiments may take the form of a computer program product ona computer-readable storage medium having computer-readable programinstructions (e.g., computer software) embodied in the storage medium.More particularly, implementations of the preferred embodiments may takethe form of web-implemented computer software. Any suitablecomputer-readable storage medium may be utilized including hard disks,CD-ROMs, optical storage devices, or magnetic storage devices.

The preferred embodiments according to the present invention aredescribed below with reference to block diagrams and flowchartillustrations of methods, apparatuses (i.e., systems) and computerprogram products according to an embodiment of the invention. It will beunderstood that each block of the block diagrams and flowchartillustrations, and combinations of blocks in the block diagrams andflowchart illustrations, respectively, can be implemented by computerprogram instructions. These computer program instructions may be loadedonto a general purpose computer, special purpose computer, or otherprogrammable data processing apparatus to produce a machine, such thatthe instructions which execute on the computer or other programmabledata processing apparatus create a means for implementing the functionsspecified in the flowchart block or blocks.

These computer program instructions may also be stored in acomputer-readable memory that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-readablememory produce an article of manufacture including computer-readableinstructions for implementing the function specified in the flowchartblock or blocks. The computer program instructions may also be loadedonto a computer or other programmable data processing apparatus to causea series of operational steps to be performed on the computer or otherprogrammable apparatus to produce a computer-implemented process suchthat the instructions that execute on the computer or other programmableapparatus provide steps for implementing the functions specified in theflowchart block or blocks.

Accordingly, blocks of the block diagrams and flowchart illustrationssupport combinations of means for performing the specified functions,combinations of steps for performing the specified functions and programinstruction means for performing the specified functions. It will alsobe understood that each block of the block diagrams and flowchartillustrations, and combinations of blocks in the block diagrams andflowchart illustrations, can be implemented by special purposehardware-based computer systems that perform the specified functions orsteps, or combinations of special purpose hardware and computerinstructions.

A preferred embodiment according to the present invention provides aswitchable fiber termination (SFT) that may be utilized as anenhancement to optical network terminations (ONTs), optical networkunits (ONUs) and other optical network devices in optical networks,including passive optical networks (PONs). The SFTs allow these devicesto be commanded to respond to a signal received by the SFT. Generally,the SFT responds by temporarily reflecting light received on a singlewavelength back into the fiber toward a test head. In other embodiments,the signal may be reproduced by the SFT and re-inserted back into thenetwork. The test head may be located at a central office (CO) or anyother location where test head can be located such as a remote terminal(RT) location. In a preferred embodiment, the test head is a PON testhead and is comprised of an optical time-domain reflectometer (OTDR).

In one preferred embodiment, the commanding of the optical networkdevices to insert or remove the response (e.g., reflection) can beaccomplished by imbedded commands that are initiated by, for example, anoptical network device's element manager system (EMS), or by a lightwave pattern initiated by the test head. The wavelength of the signalused to evoke a response from the SFT is chosen so that it is distinctfrom, and does not interfere with, voice, video, or data traffic thatmay be carried on the fiber optic cable that comprises the opticalnetwork.

The SFT allows an OTDR located as part of the PON test head to inject atest signal at the chosen wavelength into a network fiber, selectivelyenable the SFT at one of the optical devices (e.g., ONTs) connected tothe fiber, and measure the characteristics of the distribution link andconnector of the selected device. For example, the preferred embodimentsof the SFT allow the following functions to be performed while anoptical fiber is carrying normal traffic: (1) automated testing ofdistribution and drop links; (2) a centrally located test head canselectively test the individual distribution and drop links that connectto a single feeder link in an optical network; (3) a centrally locatedtest head can identify the separate distribution and drop linksconnected to a single feeder link when two or more distribution and droplinks are the same length (without the SFT device, such a test head orinstrument can only analyze the combined characteristics of multipledistribution and drop links that are of the same length); (4) physicallayer confirmation that an ONT or other optical network device is atleast partially operational and powered on without requiring thedevice's transmit laser to be operational, thus allowing the failure ofthe device's transmit laser to be identified; (5) signal loss in anONT's or other optical network device's fiber connector may beidentified and quantified therefore enabling an end-to-end (test head toinside the device) signal loss measurement including the device'sconnector loss.

FIG. 1 is an exemplary passive optical network (PON) 100 used for thetransport of voice, video and data traffic (generally referred to hereinas “data”). Exemplary PON 100 is a point-to-multipoint fiber to thepremises (FTTP) network architecture in which unpowered opticalsplitters 102 are used to enable a single optical fiber to servemultiple premises 104. PON 100 consists of an optical line termination(OLT) 106 at the service provider's central office 108 and a number ofoptical network units (ONUs) 110 and optical network terminations (ONTs)112 near or at end-users.

PON 100 takes advantage of wavelength division multiplexing (WDM), usingone or more wavelengths for downstream traffic and other wavelengths forupstream traffic. Optical network devices such as ONUs 110 and ONTs 112are comprised of one or more wavelength-division multiplexers, amongother components, that separate or combine signals of variouswavelengths. This allows for two-way traffic on a single fiber opticcable. Generally, the latest specification calls for downstream trafficto be transmitted on the 1490 nanometer (nm) wavelength and upstreamtraffic to be transmitted at 1310 nm. The 1550 nm band is generally usedfor video in case the service provider wishes to share the PON fiberwith a hybrid fiber-coax (HFC) network, which is the traditional cableTV architecture.

PON 100 is comprised of a central office node, called an optical lineterminal (OLT) 106, one or more user nodes, called optical networkterminals (ONT) 112 and optical network units (ONU) 110, and the fibers114 and splitters 102 between them, which collectively may be referredto as the optical distribution network (ODN). The OLT 106 provides theinterface between the PON 100 and a backbone network, while ONUs 110 andONTs 112 provide the service interface to end users. These services caninclude voice (plain old telephone service (POTS) or voice over IP(VoIP)), data (typically Ethernet or V.35), video, and/or telemetry(TTL, ECL, RS530, etc.). A PON 100 is a converged network, in that manyor all of these services are converted and encapsulated in a singlepacket type for transmission over the PON fiber.

PON 100 is a shared network, in that the OLT 106 sends a single streamof downstream traffic that is seen by all ONUs 110 and ONTs 112. EachONU 110 or ONT 112 only reads the content of those packets that areaddressed to it. Encryption is used to prevent unauthorized snooping ofdownstream traffic. The OLT 106 also communicates with each ONU 110 andONT 112 in order to allocate upstream bandwidth to each node. When anONU 110 or ONT 112 has traffic to send, the OLT 106 assigns a timeslotin which the ONU 110 or ONT 112 can send its packets. Because bandwidthis not explicitly reserved for each ONU 110 or ONT 112, but allocateddynamically, a PON 100 allows statistical multiplexing andoversubscription of both upstream and downstream bandwidth. This givesPON 100 yet another advantage over point-to-point networks, in that notonly the fiber but also the bandwidth can be shared across a large groupof users, without sacrificing security.

FIG. 2 is an embodiment of a PON 200 including facilities for testingthe characteristics of the optical network. In FIG. 2, a test signal 202having a designated wavelength that is addressed to a particular opticalnetwork device 204 having a SFT is inserted into the PON 200 by an OTDR206. The test signal 202 travels downstream through the fiber 208 withinthe network 200 until it reaches the designated ONT 204. The ONT 204receives the test signal and separates it from any other voice, video ordata signals. The test signal is provided to the SFT associated with theONT 204, and the SFT responds accordingly. In a preferred embodiment,the EMS of the ONT 204 is directed by the test signal 202 or by aseparate signal (not shown in FIG. 2) to activate the SFT such that itreflects the test signal 202 back into the fiber 208 as a responsesignal 210. The response signal 210 then travels back through the fiber208 to the OTDR 206 where it is received and analyzed, as is well known.In another embodiment, the SFT electronically reproduces the test signal202 with a certain degree of fidelity, which is then re-inserted backinto the fiber 208 as the response signal 210 and transmitted upstreamto the OTDR 206.

FIG. 3 illustrates an embodiment of an exemplary optical network device300 that is further comprised of an SFT, according to the presentinvention. In the embodiment of FIG. 3, a wavelength divisionmultiplexer (WDM) 302 separates a signal based on its wavelengthcomponents. For instance, a video signal on the 1550 nm wavelength isseparated and provided to a video receiver 304. A digital signal (e.g.,Internet protocol) on the 1490 nm wavelength is extracted and providedto a digital receiver 306. According to a preferred embodiment of thepresent invention, a test signal carried on the 1625 nm wavelength isextracted and provided to a SFT 308. The SFT in turn responds to thetest signal by either reflecting the test signal back to the WDM 302, orit reproduces the test signal and transmits the reproduced test signalback to the WDM 302. In this embodiment, the WDM 302 combines thereflected or reproduced test signal with any signals being transmittedat the 1310 nm wavelength by a digital transmitter 310, and sends thecombined signal back through the fiber optic cable 312.

In one embodiment, the SFT 308 is activated to respond to the testsignal by the optical network device's 300 element manager system(“EMS,” not shown), which may communicate with the device 300 via thedesignated embedded operations channel (also referred to as an overheadchannel), as is well known. For example, in normal operation of device300, the SFT may be deactivated. However, authorized personnel mayperform testing on the fiber path to the device 300 by causing the EMSto send messages to the device 300 over the overhead channel to activatethe SFT 308 at device 300. After the EMS receives a successfultransaction response from the device 300 (e.g., a response messageindicating that the SFT 308 has been activated), the EMS will send amessage to a network switching element to connect an OTDR to the PONfiber requiring a test, which will then insert, for example, a 1625 nmtest wavelength signal. In another embodiment, the SFT 308 may beactivated by a portion of the actual test signal received by the opticalnetwork device 300. The SFT may be deactivated upon completion of thetest via a deactivation message from the EMS or when a timer expires,whichever occurs first.

FIG. 4 is similar to FIG. 3; however in this instance the opticalnetwork device 400 does not have a separate video receiver. In FIG. 4video is received by the digital receiver 402 as a video over apacket-data signal (e.g., an Internet Protocol signal). Furthermore, inFIG. 4, because of the “vacant” video channel, the test signal may havedifferent wavelengths such as, for example, 1625 nm or 1550 nm.

FIG. 5 is an exemplary preferred embodiment of a SFT 500 comprising anoptical switch 502, as are well known in the art, and a mirror 504. Oneport of the optical switch 502 connects to a WDM 506, and another portterminates at the mirror 504. The WDM 506 directs light of a designatedwavelength (e.g., 1625 nm) toward the optical switch 502. The opticalswitch 502 is activated by a message from the EMS and, in turn, allowsthe light to pass from the WDM 506 to the mirror 504, where it isreflected back into the fiber 508. When the optical switch 502 isdeactivated by the EMS, the light path to the mirror 504 is interrupted.In another embodiment (not shown), the optical switch 502 is omitted andthe position of the mirror 504 is mechanically changed in order toprovide a reflected light signal back into the fiber 508. In yet anotherembodiment, the mirror 504 is replaced with an active device so thanwhen activated, light is reflected, but when deactivated, the activedevice either absorbs the light signal or does not reflect the signal.

FIG. 6 is an exemplary process of using an optical network deviceequipped with a SFT to determine characteristics of an optical networkand one or more of the components that comprise the network. The processstarts at step 600. At step 602, a test signal is injected into a fiberusing an OTDR. The test signal may include address information thatspecifies a certain optical network device. At step 604, the test signalis transmitted via the optical network to the designated optical devicehaving an SFT. At step 606, the test signal is separated from any othersignal received at the optical network device based on the test signal'scarrier wavelength (in this example, 1625 nm). At step 608, the SFT ofthe optical network device responds to the test signal and a responsesignal is re-inserted back into the fiber for upstream transmission. Theresponse may take the form of reflecting the test signal, or byelectronically or optically reproducing the test signal. At step 610,the response signal is received at the OTDR, and transmission metricsare measured. The process ends at step 612.

FIG. 7 shows an exemplary process for a SFT according to an embodimentof the invention. The process starts at step 700. At step 702, a signalis received at an optical network device having an SFT. This signalactivates or turns on the SFT. Once the SFT is activated, the processgoes to step 704 where a test signal is received at the SFT and the SFTresponds to the test signal. (Note that steps 702 and 704 may besimultaneous—the test signal may contain a signal to activate the SFT.)This response may be in the form of a reflection of the test signal, ora reproduction of the test signal. At step 706, the SFT is turned off ordeactivated. This may occur as a time-out function or be triggered bythe SFT responding to the test signal. The SFT may also be deactivatedby another signal sent to the optical network device that utilizes theSFT. The process ends at step 708.

FIG. 8 describes an exemplary process for determining characteristicsand the status of an optical network and one or more of the componentsthat comprise the optical network according to an embodiment of thepresent invention. The process starts at step 800. At step 802 a signalis inserted into an optical network to activate a designated SFT. Atstep 804, a test signal is inserted into the optical network. (Note thatsteps 802 and 804 may be simultaneous—the test signal may contain asignal to activate the SFT.) At step 806, a response signal thatoriginated from the designated SFT is received. This response signal maybe a reflection or a reproduction of the test signal. At step 808, theresponse signal is analyzed to determine the characteristics and thestatus of an optical network and one or more of the components thatcomprise the optical network. The process ends at step 810.

Many modifications and other embodiments will come to mind as a resultof the teachings presented in the foregoing descriptions of thepreferred embodiments. Accordingly, it should be understood that theinvention is not to be limited to the specific embodiments describedherein, but rather to the appended claims, and that modifications andother embodiments are intended to be included within the scope of theappended claims. Although specific terms are employed herein, they areused in an inclusively descriptive sense only and not for purposes oflimitation.

1. A fiber-optic network comprised of: one or more optical networkdevices; a central office comprised of an optical line terminationcapable of sending and receiving optical signals of one or morewavelengths; and fiber optic cable that connects the one or more opticaldevices to the central office, wherein at least one of said one or moreoptical devices include a switchable fiber termination (SFT) that isconfigured to be turned on by a signal from said optical linetermination and said SFT is configured to respond to a test signal sentto said SFT through said fiber optic cable by said optical linetermination, wherein said SFT is comprised of a switchable mirror andsaid SFT responds to said test signal by reflecting said test signalback into said fiber optic cable.
 2. The fiber optic network of claim 1,wherein said optical network device is comprised of one or more of anoptical network terminal, an optical network unit, and an opticalsplitter.
 3. The fiber optic network of claim 1, wherein said opticalline termination includes an optical time-domain reflectometer (OTDR).4. The fiber optic network of claim 1, wherein said test signal has awavelength of 1625 nanometers.
 5. The fiber optic network of claim 1,wherein said SFT receives said test signal, reproduces it, andre-injects the reproduced test signal back into said fiber optic cable.6. An optical network terminal (ONT) comprising: at least one wavelengthdivision multiplexer connected to a fiber optic cable; at least onedigital receiver; at least one digital transmitter; and a switchablefiber termination (SFT), wherein said SFT is configured to be activatedby a signal received by said ONT and said wavelength divisionmultiplexer receives an optical signal comprised of one or more signalshaving discrete wavelengths and separates said optical signal into atleast a test signal and a digital signal and said switchable fibertermination receives said test signal and responds with a responsesignal, wherein said SFT includes a switchable mirror and said responsesignal comprises said test signal reflected back into said fiber opticcable.
 7. The ONT of claim 6, wherein said test signal has a wavelengthof 1625 nanometers and said digital signal has a wavelength of 1490nanometers.
 8. The ONT of claim 6, wherein said SFT receives said testsignal, reproduces it as said response signal, and re-injects theresponse signal back into said fiber optic cable.
 9. The ONT of claim 6,wherein said digital receiver receives a signal that has a wavelength of1490 nanometers and includes video over Internet Protocol data.
 10. TheONT of claim 6 further comprising a video receiver that receives a videosignal from the wavelength-division multiplexer that has a wavelength of1550 nanometers.
 11. A method of testing a fiber-optic network whilesaid network carries data, comprising: injecting a signal into a fiberoptic cable, wherein said signal is comprised of a test signal having afirst wavelength and data signal having a second wavelength;transmitting said signal through said fiber optic network to an opticaldevice having a switchable fiber termination; separating said testsignal from said data signal at said optical device and routing saidtest signal to said switchable fiber termination, wherein saidswitchable fiber termination responds to said test signal byre-inserting a response signal back into the fiber optic cable; andreceiving and analyzing said response signal, wherein said switchablefiber termination includes a switchable mirror and responds to said testsignal by reflecting said test signal back into the fiber optic cable toform the response signal.
 12. The method of claim 11, wherein saidswitchable fiber termination responds to said test signal by reproducingsaid test signal as said response signal, and re-injecting the responsesignal back into said fiber optic cable.
 13. The method of claim 11,wherein injecting a signal into a fiber optic cable is performed usingan optical time-domain reflectometer (OTDR).
 14. The method of claim 11,wherein receiving and analyzing said response signal is performed usingan optical time-domain reflectometer (OTDR).
 15. The method of claim 11,wherein separating said test signal from said data signal at saidoptical device is performed using a wavelength-division multiplexer. 16.The method of claim 11, wherein said first wavelength is one of 1550 or1625 nanometers.
 17. The method of claim 16, wherein the secondwavelength is 1490 nanometers.
 18. A method of using an optical networkdevice equipped with a switchable fiber termination (SFT) to test anoptical network actively carrying data, comprising: receiving from theoptical network a optical signal at said optical network device, thesignal including an SFT activation message; activating the SFT as aresult of receiving the SFT activation message; receiving an opticaltest signal at the SFT; sending a response signal from the SFT inresponse to said optical test signal to the optical network; anddeactivating said SFT, wherein said SFT comprises a switchable mirror,wherein sending a response signal includes reflecting said optical testsignal back into the optical network to form the response signal. 19.The method of claim 18, wherein said optical signal includes the SFTactivation message and the optical test signal.
 20. The method of claim18, wherein sending a response signal includes reproducing said opticaltest signal and injecting the reproduced optical test signal back intosaid optical network to form the response signal.
 21. The method ofclaim 18, wherein said optical test signal has a wavelength of one of1550 nanometers or 1625 nanometers.